A light reflecting material is generally used for sign-boards, displays, backlights for liquid crystal displays, and the like. Conventionally used light reflecting sheet include a metal plate, a metal foil/plastic sheet, a metal-deposited plastic sheet, a foamed stretched PET (polyethylene terephthalate) film, and the like.
In recent years, applications of liquid crystal displays have been remarkably enlarged. Still larger growth is expected particularly in applications for liquid crystal TVs as well as in conventional use for displays in notebook personal computers. For monitors of 508 mm (20 inches) or less in size and notebook personal computers, a light guiding-type backlight is used as a light source. For liquid crystal TVs, a direct underlying-type backlight is used as a light source to attain high brightness and high resolution in medium-sized or wide screens measuring 508 mm (20 inches) or larger. In each backlight, a fluorescent lamp is used as a light source and a reflecting plate is used for efficiently guiding light from the fluorescent lamp to the liquid crystal unit. Various materials have been proposed for the reflecting plate.
In the light guiding-type backlight, a foamed PET film is placed under the light guiding plate to use as a reflecting plate. As the reflecting plate in the direct underlying-type backlight, a laminate of a foamed PET or foamed PP film and an aluminum plate, and a microcellular PET sheet are used. Among them a bent-up article of a laminate of a foamed PET film and an aluminum plate is used in many cases.
The present applicant has marketed a polycarbonate-based material for high reflecting plates developed by making use of his own technology of blending titanium oxide. The present applicant has also proposed a technology that an extruded sheet obtained from a polycarbonate resin (PC resin) composition with a high content of titanium oxide is heat-molded into a form of reflecting plate to use for the direct underlying-type backlight (for example, see Patent Document 1).
At present, a foamed reflecting film (for example, “Lumirror” ™, manufactured by Toray Industries, Inc.), which is used most frequently as a reflecting material for both direct underlying-type backlights and light-guiding type backlights, has a thickness as thin as 20 μm, so that the film exhibits no light shielding effect, and the light reflectance is also lower than that of a microcellular PET, which has begun being used as a new reflecting material. The polycarbonate-based high reflecting sheet proposed by the present applicant has higher light reflectance and light shielding effect as compared with the above-mentioned foamed reflecting film, but the light reflectance is lower that that of the microcellular PET.
Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-149623.